Homework 1: ArrayList Solution

Important

There are general homework guidelines you must always follow. If you fail to follow any of the following guidelines, you risk receiving a 0 for the entire assignment.


    1. All submitted code must compile under JDK 8. This includes unused code, so don’t submit extra les that don’t compile. Any compile errors will result in a 0.

    2. Do not include any package declarations in your classes.

    3. Do not change any existing class headers, constructors, instance/global variables, or method sig-natures. For example, do not add throws to the method headers since they are not necessary.

    4. Do not add additional public methods.

    5. Do not use anything that would trivialize the assignment. (e.g. Don’t import/use java.util.ArrayList for an ArrayList assignment. Ask if you are unsure.)

    6. Always be very conscious of e ciency. Even if your method is to be O(n), traversing the structure multiple times is considered ine cient unless that is absolutely required (and that case is extremely rare).

    7. You must submit your source code, the .java  les, not the compiled .class  les.

    8. Only the last submission will be graded. Make sure your last submission has all required les. Resubmitting will void all previous submissions.

    9. After you submit your les, redownload them and run them to make sure they are what you intended to submit. You are responsible if you submit the wrong les.


Collaboration Policy

Every student is expected to read, understand and abide by the Georgia Tech Academic Honor Code.

When working on homework assignments, you may not directly copy code from any source (other than your own past submissions). You are welcome to collaborate with peers and consult external re-sources, but you must personally write all of the code you submit. You must list, at the top of each le in your submission, every student with whom you collaborated and every resource you consulted while completing the assignment.

You may not directly share any les containing assignment code with other students or post your code publicly online. If you wish to store your code online in a personal private repository, you can use Github Enterprise to do this for free.

The only code you may share is JUnit test code on a pinned post on the o cial course Piazza. Use JUnits from other students at your own risk; we do not endorse them. See each assignment’s PDF for more details. If you share JUnits, they must be shared on the site speci ed in the Piazza post, and not anywhere else (including a personal GitHub account).

Violators of the collaboration policy for this course will be turned into the O  ce of Student Integrity.

Style and Formatting

It is important that your code is not only functional, but written clearly and with good programming style. Your code will be checked against a style checker. The style checker is provided to you, and is


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Homework 1: ArrayList    Due: See Canvas



located on Canvas. It can be found under Files, along with instructions on how to use it. A point is deducted for every style error that occurs. If there is a discrepancy between what you wrote in accordance with good style and the style checker, then address your concerns with the Head TA.

Javadocs

Javadoc any helper methods you create in a style similar to the existing javadocs. If a method is overridden or implemented from a superclass or an interface, you may use @Override instead of writing javadocs. Any javadocs you write must be useful and describe the contract, parameters, and return value of the method. Random or useless javadocs added only to appease checkstyle will lose points.

Vulgar/Obscene Language

Any submission that contains profanity, vulgar, or obscene language will receive an automatic zero on the assignment. This policy applies not only to comments/javadocs, but also things like variable names.

Exceptions

When throwing exceptions, you must include a message by passing in a String as a parameter. The message must be useful and tell the user what went wrong. \Error", \BAD THING HAP-PENED", and \fail" are not good messages. The name of the exception itself is not a good message. For example:

Bad: throw new IndexOutOfBoundsException(‘‘Index is out of bounds.’’);

Good: throw new IllegalArgumentException(‘‘Cannot insert null data into data structure.’’);

Generics

If available, use the generic type of the class; do not use the raw type of the class. For example, use new LinkedList<Integer>() instead of new LinkedList(). Using the raw type of the class will result in a penalty.

Forbidden Statements

You may not use these in your code at any time in CS 1332.

package

System.arraycopy() clone()

assert()

Arrays class Array class Thread class
Collections class

Collection.toArray()

Re ection APIs

Inner or nested classes Lambda Expressions

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Homework 1: ArrayList    Due: See Canvas



Method References (using the :: operator to obtain a reference to a method)


If you’re not sure on whether you can use something, and it’s not mentioned here or anywhere else in the homework les, just ask.

Debug print statements are ne, but nothing should be printed when we run your code. We expect clean runs - printing to the console when we’re grading will result in a penalty. If you submit these, we will take o points.

JUnits

We have provided a very basic set of tests for your code. These tests do not guarantee the correctness of your code (by any measure), nor do they guarantee you any grade. You may additionally post your own set of tests for others to use on the Georgia Tech GitHub as a gist. Do NOT post your tests on the public GitHub. There will be a link to the Georgia Tech GitHub as well as a list of JUnits other students have posted on the class Piazza.

If you need help on running JUnits, there is a guide, available on Canvas under Files, to help you run JUnits on the command line or in IntelliJ.











































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Homework 1: ArrayList



ArrayList

Due: See Canvas

You are to code an ArrayList, which is a list data structure backed by an array where all of the data is contiguous and aligned with index 0 of the array.

The ArrayList must follow the requirements stated in the javadocs of each method you must implement.

A constructor stub is provided for you to    ll out.

Capacity

The starting capacity of the ArrayList should be the constant INITIAL CAPACITY de ned in ArrayList.java.


Reference the constant as-is. Do not simply copy the value of the constant. Do not change the constant. If, while adding an element, the ArrayList does not have enough space, you should regrow the backing array to twice its old capacity. Do not regrow the backing array when removing elements.

Adding

You will implement three add() methods. One will add to the front, one will add to the back, and one will add to anywhere in the list given a speci c index. When adding to the front or the middle of the list, subsequent elements must be shifted back one position to make room for the new data. See the javadocs for more details.

Removing

You will also implement three remove() methods - from the front, the back, or anywhere in the list given a speci c index. When removing from the front or from the middle of the list, the element should be removed and all subsequent elements should be shifted forward by one position. When removing from the back, the last element should be set to null in the array. All unused positions in the backing array must be set to null. See the javadocs for more details.

Amortized E  ciency

The e ciency of methods and algorithms in this course is often analyzed using a \per operation" analysis. That is, what is the worst this algorithm can do on any one instance? However, there are times where this type of analysis is unrealistically pessimistic. For example, in this homework, the addToBack() method is O(1) for the most part except in the case of resizing, which is O(n). However, a resize operation is rare enough that it’d be misleading to say that the method is O(n).

In cases like this, we use an amortized analysis. This type of analysis adds up the cost of a se-ries of operations and then averages the cost. Here, the resize step is O(n), but since we double the capacity whenever the array gets full, we’ve put o resizing for another n add operations. So, putting that together with the common, cheap O(1) operations, we get O(1) using this analysis. Whenever this type of analysis is used, we will pre x the Big-O with the word amortized.

Equality

There are two ways of de ning objects as equal: reference equality and value equality.

Reference equality is used when using the == operator. If two objects are equal by reference equal-ity, that means that they have the exact same memory locations. For example, say we have a Person object with a name and id eld. If you’re using reference equality, two Person objects won’t be considered equal unless they have the exact same memory location (are the exact same object), even if they have the same name and id.

Value equality is used when using the .equals() method.  Here, the de nition of equality is custom


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Homework 1: ArrayList    Due: See Canvas



made for the object. For example, in that Person example above, we may want two objects to be con-sidered equal if they have the same name and id.

Keep in mind which makes more sense to use while you are coding. You will want to use value equality in most cases in this course when comparing objects. Notable cases where you’d use reference equality include checking for null or comparing primitives (in this case, it’s just the == operator being overloaded).

Di erences between Java API and This Assignment

Some of the methods in this assignment are called di erent things or don’t exist in Java’s ArrayList class. This won’t matter until you tackle coding questions on the rst exam, but it’s something to be aware of. The list below shows all methods with a di erent name and their Java API equivalent if it exists. The format is assignment method name ) Java API name.

addAtIndex(int index, T data) ) add(int index, T data) addToFront(T data) ) no explicit method

addToBack(T data) ) add(T data)

removeAtIndex(int index) ) remove(int index) removeFromFront() ) no explicit method

removeFromBack() ) no explicit method





































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Homework 1: ArrayList    Due: See Canvas



Grading

Here is the grading breakdown for the assignment. There are various deductions not listed that are incurred when breaking the rules listed in this PDF and in other various circumstances.

Methods:



addAtIndex
15pts


addToFront
11pts


addToBack
11pts


removeAtIndex
11pts


removeFromFront
7pts


removeFromBack
7pts


get
6pts


isEmpty
3pts


clear
4pts


Other:



Checkstyle
10pts


E  ciency
15pts


Total:
100pts



Provided

The following    le(s) have been provided to you. There are several, but we’ve noted the ones to edit.

    1. ArrayList.java

This is the class in which you will implement the ArrayList. Feel free to add private helper methods but do not add any new public methods, inner/nested classes, instance vari-ables, or static variables.

    2. ArrayListStudentTest.java

This is the test class that contains a set of tests covering the basic operations on the ArrayList class. It is not intended to be exhaustive and does not guarantee any type of grade. Write your own tests to ensure you cover all edge cases.


Deliverables

You must submit all of the following le(s). Make sure all le(s) listed below are in each submission, as only the last submission will be graded. Make sure the lename(s) matches the lename(s) below, and that only the following le(s) are present. The only exception is that Canvas will automatically append a -n depending on the submission number to the le name(s). This is expected and will be handled by the TAs when grading as long as the le name(s) before this add-on matches what is shown below. If you resubmit, be sure only one copy of each le is present in the submission. If there are multiple les, do not zip up the les before submitting; submit them all as separate les.

Once submitted, double check that it has uploaded properly on Canvas. To do this, download your uploaded le(s) to a new folder, copy over the support le(s), recompile, and run. It is your sole respon-sibility to re-test your submission and discover editing oddities, upload issues, etc.

    1. ArrayList.java



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